you do not want the vehicle to be part in race, right? easily done.
go to your vehicles folder, i. e.:
C:\Program Files (x86)\Steam\SteamApps\common\Automobilista\GameData\Vehicles
there, each car class/mod has it's own folder. search for the right one and open it. then search for the team and remove/delete it. if you just want one driver to be deleted, open the folder of the team and delete just the files concerning the driver. you can open the veh-files first in order to see if it is the driver you want to get rid of.
always backup all the files before. cheers.